I never complete her quest. I go and get the scroll, and then just leave. After that, every time I fast travel she matrialises next to me and gives a random quip. My favorite is when I travel to Whiterun or some other city and she'll just say, "Sometimes I just like to watch them burn." It makes me picture all the civillians looking at her all like, "Wow, that bitch has some serious problems."

I did, but after that she just deciphers the scroll ad infinitum. I checked online and people were saying she was difficult to have as a permanent follower because she didn't have the voice files for it, so the game didn't like her being moved into the followers faction. Is the only way right now to have her be a permanent follower to accept her quest and not complete it?